This invention relates generally to coatings for ink jet transparencies, and ink jet paper; and more specifically, the present invention is directed to the use of coatings for various substrates so as to enable the achievement of acceptable optical density while simultaneously allowing the rapid drying of the inks selected for development. The coated substrates, inclusive of the transparencies and papers, generated in accordance with the present invention are particularly useful in ink jet printing processes. Also, the coated papers can be useful in electrostatographic imaging processes.
Ink jet printing systems are well known thus, for example, there is described in U.S. Pat. No. 3,846,141 a composition useful in ink jet printing comprised of an aqueous solution of a water-soluble dye and a humectant material formed of a mixture of a lower alkoxy triglycol, and at least one other compound selected from the group consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, and glycerol. According to the disclosure of this patent, the viscosity of the printing inks is subjected to little variation with use in that water is lost by evaporation during recirculation of the ink composition through the jet printer. Moreover, apparently the humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the orifice or nozzle during down time of the printer such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice usually of a diameter of 0.0024 inches, which is energized by magneto restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example paper, and is controlled to form printed characters in response to video signals deirved from an electronic character generator and in response to an electrostatic deflection system.
Also, there is disclosed in U.S. Pat. No. 4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, U.S. Pat. No. 4,196,007 describes an ink jet printing composition containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Other patents disclosing aqueous inks for ink jet printing include U.S. Pat. Nos. 4,101,329; 4,290,072; and 4,299,630.
Further, disclosed in U.S. Pat. No. 4,273,602, are heat sensitive recording materials comprised of a support sheet of a thickness of from 5 to 40 microns containing thereon a heat sensitive transfer layer with a phenolic material, a colorless or precolored material which reacts with the phenolic material to form color upon application of heat, and a heat fusible material having a melting point of 40.degree. C. to 150.degree. C., with an image receiving sheet superimposed on the surface of this layer. It is indicated in this patent that heat sensitive transfer layers can be formed from waxes or resins of low molecular weight, with colored dyes dispersed therein, however, apparently there are problems associated with such a method in that part of the layer transfers to ordinary paper causing undesirable staining and a decrease in contrast between letters and the background. Accordingly, the recorded letters cannot be easily read.
Also known is the preparation of transparencies by electrostatic means. There is thus disclosed, for example, in U.S. Pat. No. 4,370,379 a method for preparing an original for projection according to electrophotographic processes. More specifically, it is indicated in this patent that the conventional method for preparing a projection original for an overhead projector, (a transparent sheet), according to electrostatic photography comprises transferring a toner image formed on a photosensitive plate onto a stretched polyester film, and fixing the transferred toner image on the film by heat. Various plastic films can be used for this purpose including biaxially stretched polyester film. It is further indicated in this patent that the transfer film selected for electrostatic photography is comprised of a film substrate which is transparent such as a biaxially stretched polyethylene terephthalate film including Mylar films.
Moreover, there is disclosed in U.S. Pat. No. 4,234,644, a composite lamination film for electrophoretically toned images deposited on a plastic dielectric receptor sheet comprising in combination an optically transparent flexible support layer, and an optically transparent flexible intermediate layer of a heat softenable film applied to one side of the support layer wherein the intermediate layer possesses good adhesion to the support layer. It is indicated in this patent that the support layer 11 can be prepared from various suitable substances including polycarbonates, polysulfones, polyethylene terephthalates, Mylars, and the like.
While the above transparencies are suitable for their intended purposes, there remains a need for ink jet transparencies and for coatings for ink jet paper which will enable the rapid drying of the inks selected. Additionally, there remains a need for coatings for ink jet transparencies which are compatible with the supporting substrate and the ink compositions selected for marking.